The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
As known per se, an aircraft propulsion unit conventionally comprises a turbojet engine housed inside a nacelle.
The nacelle generally has a tubular structure comprising an air intake upstream of the turbojet engine, a median section intended to surround a fan of the turbojet engine and its casing, and a downstream section intended to surround the combustion chamber of the turbojet engine and accommodating, where appropriate, thrust reversal means. It may be terminated by an ejection nozzle whose outlet is located downstream of the turbojet engine.
For the purpose of reducing mass and increasing performances, in particular mechanical performances, the aeronautical industry increasingly uses composite materials to produce structural parts and/or panels.
Such elements are generally made from sets of fibrous plies embedded in a matrix made of organic or ceramic materials. These elements can be monolithic or enclose a core made of another material.
This is the case for example in the acoustic panels used to reduce the noise emissions generated by the turbojet engine, and of which is common to equip several portions of the nacelle and/or of the turbojet engine.
These portions of the nacelle and/or of the turbojet engine may be, for example, an inner surface of the air flow path for a bypass turbojet engine, a nozzle or ejection cone surface, an air intake inner panel, etc.
Such acoustic panels are in the form of a sandwich-type panel comprising at least a cellular core, for example a honeycomb-like structure, covered with a perforated or acoustically porous outer skin (called acoustic skin) and with a solid inner skin (called support or structural skin). This set forms a resonator.
The skins of these panels can be made of composite material comprising a set of fibers (superposition of fibrous plies), embedded in a matrix of organic or ceramic origin.
More particularly, the ceramic-matrix composites, also known as “CMC”, are composite materials that are formed by a set of commonly ceramic fibers associated with an equally ceramic matrix.
The ceramic composites have interesting properties, in particular tensile strength, flexural strength and breakage resistance properties, heat resistance properties, and anti-corrosion properties.
Also, the ceramic composites are lightweight materials whose density is close to that of aluminum.
Among the ceramic composites, the oxide-based ceramic composites (aluminas, alumino-silicates in particular) are known, they form good electrical insulators and also have an interesting thermal insulation capacity, a good heat resistance and a good mechanical fatigue strength.
Although the ceramic composites have many advantages, their manufacture is delicate.